Method and apparatus for determining the proximity of a tms coil to a subject&#39;s head

ABSTRACT

A proximity sensor for a transcranial magnetic stimulation (TMS) system detects the proximity of a TMS coil assembly to a position at which the coil is to receive pulses during TMS treatment and provides feedback to the operator so that the operator may adjust the coil assembly to maintain optimal positioning during treatment. A flexible substrate containing a sensor or sensor array is disposed between the TMS coil assembly and the position such that the coupling of the TMS assembly to the position may be detected by the sensor(s). Sensor outputs are processed by signal processing circuitry to provide an indication of whether the TMS coil assembly is properly disposed with respect to the position during TMS treatment. A display provides an indication of how to adjust the TMS coil assembly to improve the positioning of the TMS coil assembly.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. application Ser. No.10/825,043 filed on Apr. 15, 2004 which is incorporated herein byreference as if fully set forth.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for determiningthe proximity of a TMS treatment coil to a position on a patient and,more particularly, to a proximity measurement and contact positioningapparatus and method for determining whether a TMS coil is properlyseated against a patient's head during treatment.

BACKGROUND OF THE INVENTION

Current methods of placement and positioning of coils for TranscranialMagnetic Stimulation (TMS) studies are either manual methods orapproaches designed for research that require expensive and compleximaging or computational systems to determine three dimensional spatialcoordinates for positioning reference. These techniques have severeclinical limitations. The manual methods do not provide a convenientmeans for repeated and accurate placement, while the three dimensionalspatial methods based on imaging modalities are expensive, timeconsuming, and not conducive to clinical use. Accordingly, the presentassignee has developed a positioning technique for clinical use thatprovides a simple way for the operator to perform repeated and accuratecoil placement for TMS studies and treatments in a time-efficient andinexpensive manner. This TMS coil positioning technique is described inU.S. patent application Ser. No. 10/752,164, filed on Jan. 6, 2004, thecontents of which are incorporated herein by reference.

Further techniques are also needed to comfortably hold the coil in placeat the treatment position throughout a therapy session. Closeapproximation of the TMS stimulation coil to the patient's head duringlocation of the motor threshold position or during therapy applicationsis critical to ensure that the proper magnetic field intensity isapplied to the patient. The coil must remain in contact with the scalpthroughout the application of stimulation pulses. The clinician does notcurrently have a good method to ensure that the coil is in contact, andhas no means of feedback as to whether the coil has moved away from thescalp during treatment. If the coil movement occurs during the motorthreshold (MT) level determination procedure, an inappropriately highpower setting may be used. On, the other hand, if the movement occursafter MT determination and during the treatment session, aninappropriately low magnetic field may be applied to the patientresulting in possibly reduced efficacy.

Current methods of holding the TMS coil against the patient's headinclude holding it by hand throughout the TMS procedure, supporting itwith a mechanical arm and relying on the patient to remain stillrelative to the coil throughout the procedure, and mechanical alignmentmethods (e.g. Brainsight™ system) that physically restrain the patient'shead against the coil. However, such solutions do not ensure that thecoil is initially positioned against the patient's head or that the coilstays against the head throughout the procedure. These methods rely onthe clinician to visually observe that contact is being made. Suchobservations may not be reliably be made continuously throughout theprocedure. In addition, there are no solutions that provide feedback tothe operator as to the state of coil contact.

Many companies provide pressure and contact sensors, including formedical applications (e.g. Tekscan), but these sensors are not designedfor optimal use in the unique environment of a pulsed high magneticfield or for TMS use, and the present inventors are not aware that suchsensors have been used to assist the clinician in maintaining TMS coilcontact with a subject's head throughout treatment. Accordingly, anapparatus and technique for detecting that a TMS coil is and remains incontact with the patient throughout the TMS therapy procedure is needed.The present invention addresses this need in the art.

SUMMARY OF THE INVENTION

The present invention addresses the above-mentioned needs in the art byproviding a transcranial magnetic stimulation (TMS) system having a TMScoil assembly, a pulse generating device that applies pulses to the TMScoil assembly during TMS treatment of a patient, a sensor disposedbetween the TMS coil assembly and the position at which pulses areapplied (e.g., motor threshold or TMS treatment position) that detectsproximity of the TMS coil assembly to the position, and signalprocessing circuitry that processes outputs of the sensor to provide anindication of whether the TMS coil assembly is properly disposed withrespect to the position during application of pulses to the TMS coilassembly. The indication is preferably provided to a display device thatindicates to an operator of the TMS device whether the TMS coil assemblyis properly positioned at the position and/or in which direction to movethe TMS coil assembly to the position in the event that the TMS coilassembly is not at the position. The indication also may be provided toa sound generator that generates a sound that is detected to indicate toan operator of the TMS device whether the TMS coil assembly is properlypositioned at the position.

The sensor comprises a plurality of sensors, such as a sensor array,that may be disposed in or on a flexible substrate that is, in turn,placed between the TMS coil assembly and the position to determine ifthe TMS coil assembly is properly positioned with respect to theposition during TMS therapy.

In a first embodiment, the sensors may comprise membrane switches thatchange state when depressed. The membrane switches may, in turn, includeresistive strips that provide an output voltage that varies withposition of contact on the membrane switches. The membrane switches alsomay include an array of separators between respective conductive filmsso as to form a touch screen.

In a second embodiment, the sensors may comprise variable resistancesensors that provide an output signal that is proportionate to appliedcontact pressure, whereby a change in resistance above a predeterminedthreshold is identified as an indication of contact.

In a third embodiment, the sensors may comprise one or more fluiddisplacement sensors and fluid filled bladders connected by anon-compressible manifold to the fluid displacement sensors such thatcompression of a bladder causes a change in pressure at the fluiddisplacement sensor. Preferably, the fluid filled bladders are disposeddirectly over respective pole faces of a TMS coil of the TMS coilassembly and fluid in the fluid filled bladders is a substantiallynon-electrically-conductive fluid so as not to interfere with the TMSfield.

In a fourth embodiment, the sensors may comprise optical fibers thatcross the position and an optical grating disposed on the substrate,whereby light passing through the optical fibers is deflected whencontact is made by the TMS coil assembly to the position so as to changean amount of light reflected by the optical grating. The reflected lightis detected by an optical detector.

In a fifth embodiment, the sensors may comprise an acoustic device thatproduces an acoustic sound (that may or may not be in the human audiblerange) when a TMS coil of the TMS coil assembly is pulsed and reduces anamplitude of the sound as the acoustic device is compressed by the TMScoil assembly against the position. Acoustic sensors detect the soundand provide a proportionate voltage signal to the signal processingcircuitry for a determination as to whether an amplitude change hasoccurred. Acoustic sensors are not necessary if a conductive disk isconfigured to “rattle” in a cavity when a magnetic field is applied butis inhibited from “rattling” when the sensor is compressed against thepatient.

In a sixth embodiment, the sensors may comprise inductive couplingsensors including at least one tuned coil mounted at the position on thepatient. A tuned frequency of the tuned coil is selected to shift whenthe TMS coil assembly is in physical contact with the position. A shapeof the tuned coil may be distorted when compressed against the positionby the TMS coil assembly such that the resulting induced current in thetuned coil may be detected by the signal processing circuitry to providethe indication of whether the TMS coil assembly is in contact with thepatient at the position.

In a seventh embodiment, the sensors may comprise EEG leads that sensecurrents induced in the position by a TMS pulse from the TMS coilassembly. In this embodiment, the signal processing circuitry comparesamplitudes of sensed currents to a threshold to obtain an indication ofwhether the TMS coil assembly is properly disposed with respect to theposition during TMS treatment.

In an eighth embodiment, the sensors may comprise temperature sensors.In this embodiment, the signal processing circuitry processes outputs ofthe temperature sensors to determine if a temperature difference betweenrespective temperature sensors is above a predetermined threshold of ifthe measured temperature of one or more of the temperature sensorsunexpectedly changes significantly. The predetermined threshold is setsuch that movement of a temperature sensor from against the head to awayfrom the head, for example, causes a temperature change that is abovethe threshold while a change in sensed temperature when in the propercontact position does not exceed the threshold and may instead be usedas a zeroed baseline temperature.

In a ninth embodiment, the sensors may comprise a loop of conductingmaterial placed at the treatment position (e.g., affixed to thepatient's scalp). When the TMS coil assembly is in proximity to the loopof conducting material, a voltage is induced therein when pulses areapplied to the TMS coil assembly.

In a tenth embodiment, the sensors comprise an acoustic sensor (in orout of the audible range) that detects acoustic waves generated when apulse is applied to the TMS coil assembly and that are mechanicallycoupled to the patient's skull and transmitted to the acoustic sensor.Decoupling of the TMS coil assembly from the patient's head causeschanges in the acoustic waves that are detected by the acoustic sensor.

Other currently available sensor embodiments may be implemented by thoseskilled in the art based on the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become apparent tothose skilled in the art based on the following detailed description ofthe drawing figures, of which:

FIG. 1A illustrates TMS system for TMS therapy using the coil positionsensing system of the invention.

FIG. 1B illustrates the attachment of a flexible circuit substratecontaining proximity sensors to the respective coil faces of the TMScoil assembly for detecting the proximity of the TMS coil to theposition at which pukes are to be supplied by the TMS coil assembly inaccordance with the invention.

FIG. 2 illustrates a general overview of the signal processingelectronics for TMS coil proximity sensing in accordance with theinvention.

FIG. 3A illustrates a sample operator display indicating poor contactwith the patient's scalp.

FIG. 3B illustrates a sample operator display indicating good contactwith the patient's scalp.

FIGS. 4A and 4B illustrate membrane switches in the no contact (FIG. 4A)and contact (FIG. 4B) positions for use as proximity sensors inaccordance with the invention.

FIG. 4C illustrates an array of membrane switches fabricated on aflexible substrate for application to the face of the TMS coil assemblyin accordance with the invention.

FIG. 5 illustrates a system configuration employing an array of membraneswitches in accordance with the invention.

FIGS. 6A and 6B illustrate a sample micro slide embodiment in which apre-bent actuator arm causes an opaque sliding arm to slide between alight source and an optical detector when depressed.

FIG. 7 illustrates a multiplexing data acquisition circuit for samplingvariable resistance force sensors configured in an array in accordancewith the invention.

FIG. 8A illustrates a plan view of a strip sensor before compression.

FIG. 8B illustrates a cross-section of a strip sensor after compression.

FIG. 9 illustrates an embodiment in which electrodes of a strip sensorare separated by an array of separators or non-conductive dots to createa touch screen sensor.

FIG. 10 illustrates an embodiment in which a loop or loops of conductingmaterial may be affixed to the patient's head at the motor threshold(MT) position andlor the position for depression treatment.

FIG. 11A illustrates fluid displacement sensors fabricated on aflexible, disposable substrate for placement on the TMS coil assemblyfor proximity detection in accordance with the invention.

FIG. 11B illustrates the fluid displacement sensors of FIG. 11Amanufactured on the same physical substrate as an e-shield device foruse in TMS applications in accordance with the invention.

FIGS. 12A-12C illustrate an optical fiber sensor embodiment in whichlight is directed via an optical fiber (FIG. 12A) toward a fiber Bragggrating (FIG. 12B) where the light is deflected by fiber(s) of the fiberBragg grating as illustrated in FIG. 12C so as to affect lighttransmission efficiency.

FIG. 12D illustrates shifting of the reflectance peak to longerwavelengths by the optical fiber sensor of FIGS. 12A-12C.

FIG. 13A illustrates a sample acoustic sensor embodiment in whichflexible membranes in as non-contact position are separated by anacoustic channel that, in turn, connects an acoustic source to an astransducer.

FIG. 13B illustrates that when the flexible membranes of FIG. 13A arepressed (against the head, for example), the acoustic channel isdisrupted, thereby reducing the sound in magnitude and/or causing afrequency shift.

FIG. 14A illustrates an embodiment of a device including flexiblemembranes separated by spacers so as to define a cavity including aconductive disk that rattles within the cavity when the ambient magneticfield is pulsed.

FIG. 14B illustrates immobilization of the conductive disk of FIG. 14Aso as to significantly damp the rattling sound when the device iscompressed against the patient.

FIG. 15 illustrates an embodiment in which sound waves generated bypulsing of the TMS coil are coupled to the patient's head andtransmitted through the skull to an acoustic transducer applied to thepatient's head at a convenient location (typically not directly beneaththe coil), whereby decoupling of the TMS coil from the patient's headchanges the detected acoustic signal.

FIG. 16A illustrates a sensor embodiment implementing inductive couplingsensors whereby a tuned coil is mounted to the substrate of the TMS coilassembly.

FIG. 16B illustrates tuned frequency shifts by the embodiment of FIG.16A when the substrate and TMS coil assembly are in physical contactwith the patients head.

FIG. 17 illustrates an embodiment in which EEG-type leads andelectrodes, or their equivalents, may be used to sense currents inducedin the scalp by the TMS magnetic pulse.

FIG. 18 illustrates an embodiment in which temperature sensors (e.g.,thermistors, thermocouples) are applied near the two critical contactareas on the substrate and the outputs provided to processing circuitryfor a determination of whether the detected temperatures track eachother or if there is an abrupt temperature change indicating a change incontact of one or more of the sensors with the skull.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A detailed description of an illustrative embodiment of the presentinvention will now be described with reference to FIGS. 1-18. Althoughthis description provides detailed examples of possible implementationsof the present invention, it should be noted that these details areintended to be exemplary and in no way delimit the scope of theinvention.

The present invention is designed to sense the positioning of a TMS coilused for treatment of central nervous system disease states using TMStherapies. While an exemplary embodiment of the invention is describedwith respect to the excitatory stimulation of the left prefrontal cortexfor the treatment of depression, those skilled in the art willappreciate that the apparatus and techniques of the invention may beused to apply TMS therapies to many other central nervous system targetsfor the treatment of numerous other central nervous system diseases. Forexample, the TMS coil position sensing device of the invention may beused to sense the positioning of the TMS coil over the right prefrontalcortex of a patient for low frequency inhibitory stimulation in thetreatment of depression. Those skilled in the art will furtherappreciate that the TMS coil position sensing device of the inventionalso may be used to sense the positioning of a TMS coil for thetreatment of: epilepsy (above seizure locus), schizophrenia (atWernicke's Area), Parkinson's Disease, Tourette's Syndrome, AmyotrophicLateral Sclerosis (ALS), Multiple Sclerosis (MS), Alzheihmer's Disease,Attention Deficit/Hyperactivity Disorder, obesity, bipolardisorder/mania anxiety disorders (panic disorder with and withoutagoraphobia, social phobia a.k.a. Social Anxiety Disorder, Acute StressDisorder, Generalized Anxiety Disorder), Post-traumatic Stress Disorder(one of the anxiety disorders in DSM), obsessive compulsive disorder(one of the anxiety disorders in DSM), pain (migraine, trigeminalneuralgia), chronic pain disorders (including neuropathic pain such aspain due to diabetic neuropathy, post-herpetic neuralgia, and idiopathicpain disorders such as fibromyalgia and regional myofascial painsyndromes), rehabilitation following stroke (neuro plasticityinduction), tinnitus, stimulation of implanted neurons to facilitateintegration, substance-related disorders (dependence and abuse andwithdrawal diagnoses for alcohol, cocaine, amphetamine, caffeine,nicotine, cannabis), spinal cord injury and regeneration/rehabilitation,head injury, sleep deprivation reversal, primary sleep disorders(primary insomnia, primary hypersomnia, circadian rhythm sleepdisorder), cognitive enhancements, dementias, premenstrual dysphoricdisorder (PMS), drug delivery systems (changing the cell membranepermeability to a drug), induction of poem synthesis (induction oftranscription and translation), stuttering, aphasia, dysphagia,essential tremor, Magnetic Seizure Therapy (MST), and other centralnervous system disorders that may treated by the application of amagnetic field at particular locations in the brain. Of course, in eachcase, the treatment positions may vary; however, in each case theposition sensing device of the invention is useful in maintaining theTMS coil at the treatment position during therapy.

Overview

FIG. 1A illustrates a system 10 for TMS therapy in accordance with theinvention. As illustrated, a patient is placed in a comfortablereclining position with respect to the system 10. An articulating arm 12allows the operator to adjust the TMS coil assembly 20 so that the TMScoil assembly 20 rests against the patient's head at the appropriateposition (e.g., motor threshold or TMS treatment positions). Duringtreatment, pulses are generated by pulse generating apparatus (notshown) in casing 30 and applied to TMS coil assembly 20 for generationof a magnetic field at the position. A display 40 permits the operatorto interface with the pulse generating apparatus and to monitor thepositioning of the TMS oil assembly 20 with respect to the position aswill be described in more detail below.

In accordance with the present invention, pressure and/or contactsensors 50 are placed on a circuit substrate 60 that is, in turn, placedby the clinical operator between the contact surfaces of the TMS coilassembly 20 and the patient's head. Preferably, the circuit substrate 50is flexible and disposable; however, the sensors need not be disposableor separate from the TMS coil assembly 20. As illustrated in FIG. 1B,the flexible circuit substrate 60 may be attached to respective coiltreatment faces 22 and 24 of the TMS coil assembly 20 mechanically orwith temporary adhesive. The sensors 50 provide output signals (analog,digital or optical) to signal processing electronics and further to ananalytical processor that assesses the validity of the signal beforepassing the signal to a user interface that provides feedback to theoperator (graphic, indicator lamp, or audible) on, for example, display40 that contact is either proper or improper. Additionally, the operatormay be provided with guidance on, for example, display 40 as to whereand bow to move the TMS cod assembly 20 to achieve proper contact (e.g.tilt up or down, rotate left or right, etc.). There are many suitablesensing technologies that may be used for the detection of contact aswill be explained below with respect to the exemplary embodiments.

System Functionality

As illustrated in FIG. 2, the outputs of a flexible sensor or sensorarray 70 of sensors 50 that has been placed on the coil treatment faces22, 24 of the TMS coil assembly 20 so as to be adjacent the patient'shead when the TMS coil assembly 20 is in the desired position areprocessed by signal processing electronics 80 to provide appropriatefiltering and the like. The signal processing electronics is dependentupon the specific type of sensor technology used but typically includesan analog signal preamplifier followed by appropriate filtering and gainadjustment. For optical implementations, some of the processing may bedone optically (e.g. filtering, polarization, wavelength separation).The processed outputs are provided by signal processing electronics tovalid contact analysis circuit 90 to determine whether the contact withthe patient is proper (e.g., the signal is compared to thresholds). Thevalidation of proper contact is performed by either analog or digitalcircuitry, or by software. These analytical algorithms depend on thenature of the artifact inherent with each type of sensor and thephysical arrangement on the flexible substrate 60. The output of circuit90 is then fed back to the user for display, for example, on displaydevice 40. User feedback 100 may be audible, graphical, numeric, or a“go-no go” indicator. Graphic feedback may include a display of areas ofphysical contact, bar graphs indicating pressure levels at the criticalareas, or pressure maps. The latter would require an array of sensors 70on the sensing substrate 60 to produce a map of the type shown by way ofexample in FIGS. 3A and 3B, where FIG. 1A indicates poor contact withthe patients scalp and FIG. 3B indicates good contact with the patient'sscalp. As illustrated, this display may be useful in guiding theoperator to reposition the TMS coil assembly 20 to improve scalpcontact. Audible feedback to the operator also may be provided.

FIGS. 3A and 3B illustrate a presently preferred embodiment in which thedisplay 40 comprises a color LCD screen (or equivalent) of a grid map ofthe contact pressure across the coil pole treatment faces 22, 24. Thisis achieved by mapping the signals from the array of sensors 70 to thedisplay grid of the display 40 with compressed sensors displayed in onecolor (e.g. green—light gray) and non-compressed sensors in anothercolor (e.g., red—dark gray). In FIGS. 3A and 3B, the black circles 105indicate the critical areas beneath the coil pole treatment faces 22, 24where good contact is desired. Ideally, all the indicators within thesecircles should be green/light gray representing a full contact status.Analysis soft are also may be employed to want the operator if anyred/dark gray pixels appear in the circles 105, so that repositioningcan be done and the TMS procedure continued.

Sensing Technology Options

Many different sensor technologies may be used in accordance with theinvention. Presently preferred embodiments and possible implementationsare described in more, detail below. These embodiments are not intendedto be all-inclusive. Those skilled in the art will appreciate that othercomparable commercially available technologies may be used as well asfuture improvements to such sensing technologies as they becomeavailable.

Membrane Switches

As illustrated in FIGS. 4A and 4B, membrane switches 110 are formed bymounting two conducting films or membranes 120, 130 in a parallelarrangement and separating the membranes 120, 130 by a gap 140 formed bya third, intermediate layer 150. The gap 140 is filled with a dielectricmaterial such as air, a resistive fluid, or a gel. As illustrated inFIG. 4B, pressure applied to the membrane switches 110 causes the layersto approximate, and contact each other. When the two conductive layers120, 130 touch, electrical contact is made which is sensed as describedbelow. The size and thickness of each sensor is selected to optimizesensitivity.

For TMS applications, an array of such switches 110 is fabricated on aflexible substrate 60 such as that illustrated in FIG. 4C that isapplied to the coil pole treatment faces 22, 24 of the TMS coil assembly20. The switches 110 are carefully positioned on this substrate 60 sothat they will detect that the patient's head is completely contactingthe surface of the TMS coil of the TMS coil assembly 20 near the centersof the coil pole treatment faces 22, 24 as shown. For example, an arrayof four or eight switches 110 can be placed in the area of each coilpole treatment face 22, 24 as illustrated in FIG. 4C and the outputsprovided to connectors 155 for provision to the signal processingelectronics 80. This arrangement helps in detecting partial contact bybeing mapped to a graphical display on display 40 to aid the operator inpositioning the TMS coil assembly 20. The use of a single switch 110 ateach coil pole treatment face 22, 24 does not provide the informationneeded to assist the operator in positioning the coil. Instead, only a“go-no go” signal is provided. While this is useful, an output thatfacilitates repositioning indicating which direction to move the coil toachieve proper contact) is preferred. Accordingly, it is desired to usemultiple switches 110 to cover the treatment area. Conductive films 120,130 of sufficient resistance should be used to reduce eddy currents andto accelerate their decay. Additionally, the conductive films 120, 130should be patterned to reduce the flow of eddy currents using techniquesknown to those skilled in the art.

A system configuration employing an array 160 of membrane switches 110is shown in FIG. 5. In this configuration, the array 160 of membraneswitches 110 provides outputs that are debounced and isolated by aconventional debounce circuit 170 and provided to a status detection anddigital interface circuit 160 to remove detection artifacts before beingprovided to a computer processor 190 that is used to acquire a set ofsignals that have been processed from the membrane switch array 160.Contact detections accomplished by applying a voltage across the upperand lower membranes 120, 130 of each switch 110 of the switch array 160.When contact is achieved, current flows and is detected by a currentsensing circuit within status detection and digital interface circuit180. Typically, the signal is first debounced by debounce circuit 170,and if contact is maintained for a specified period of time (e.g. 50milliseconds), it is assumed to be a valid contact. This status is thencommunicated by circuit 180 to the processor 190. Due to the uniquepulsed magnetic field in the proximity of the switches, the detectedsignal should be filtered or gated by signal detection and digitalinterface circuit 180 to avoid detection artifacts. The processed outputof microprocessor 190 may be provided to display driver 200 for drivinggraphical display 210 which may be, for example, on display 40. A remotecontact status indicator 220 may also be used to indicate the state ofcontact (on or off).

One skilled in the art would further appreciate that micro could beconstructed of non-conductive material (e.g. plastic) and applied to thesubstrate 60 including the membrane switch array 160. This slidearrangement provides two functions: amplification of the compression duecontact, and allowing remote location of a motion sensor away from thecritical area near the coil poles. There are a number of mechanicalarrangements that can achieve this. FIGS. 6A and 6B illustrate a samplemicro slide embodiment in which a pre-bent actuator arm 222 causes anopaque sliding arm 224 to slide between a light source 226 and an opticit detector 228 when depressed. As shown in FIG. 6A light from lightsource 226 is detected by optical detector 228 when the actuator arm 222is not depressed, while, as shown FIG. 6B, light from light source 226is blocked by opaque sliding arm 224, and hence not detected by opticaldetector 228, when the actuator arm 222 is depressed into a compressedposition. Thus, compression of the substrate membranes 120, 130 causesthe opaque sliding arm 224 to move along the face of the substratemembranes 120, 130 in a direction along the coil pole treatment faces22, 24. This motion can then be detected optically as indicated in FIG.6A, or by other means known to those skilled in the art.

Variable Resistance Sensors

As known by those skilled in the art, force sensors may be fabricatedusing resistive pastes. Similarly, strain gauges may be manufactured bypatterning a metal film to form a resistor on an elastic layer. Contactpressure distorts the resistor and the layer. This distortion causes achange in the resistance of the film resistor that is detected using abridge circuit. A threshold resistance is selected to indicate contact.As is the case with membrane switches 110, the pulsed magnetic field inthe proximity of the sensors must be considered when designing thesensor and detection circuit. High impedance designs are preferable tominimize induced current, and conductive loops are eliminated or keptvery small in cross section to minimize induced eddy currents. Either ofthese variable resistance technologies may be fabricated into sensorarrays 100 as described above for the membrane switch case with similarfunctional advantages. However, signal processing, detection and signalvalidation are different than the membrane switch 110, otherwise thesystem configuration is very comparable to that shown in FIG. 5.

A variable resistance sensor provides a continuous signal (i.e. voltage)that is a proportionate to or a monotonic function of applied pressure.Signal processing by circuit 180 and microprocessor 190 in this casecomprises filtering, applying a calibrated setting a gain and offset,and gating to synchronize with the magnetic pulse. A calibrated pressurevalue can be determined by digitizing (i.e. via A/D converter) theprocessed sensor signal, the digital value being sampled and sent to theprocessing computer 190 as shown in FIG. 5. Calibrated pressure valuesthen could be displayed to the operator on display 40 or, alternatively,a threshold detection circuit may be used to decide if contact has beenachieved.

FIG. 7 depicts a multiplexing data acquisition circuit 230 for samplingvariable resistance force sensors 240 configured in an array 250.Variable resistance force sensors 240 suitable for the presentapplication are available from Tekscan (e.g., “Flexiforce”). Thesesensors 240 are typically fabricated by applying a silver layer on eachof two substrates. A resistive paste is placed between these silvercontact areas and the assembly sealed and mechanically stabilized. Theresistance between the two contacts changes with applied pressure. Thecontacts can be of a custom geometry and can be fabricated in largearrays. These structures lend themselves well to the desire for a lowcost, flexible and disposable design. For TMS applications, singlesensors 240 may be placed at each of the critical contact areas, or anumber of sensors 240 may be placed at each location (e.g. FIG. 7). Theadvantage of employing a number of sensors 240 is that feedback can beprovided to the operator as to which way to move the TMS coil assembly20 to achieve better contact. One proposed implementation is to use abroad array or grid arrangement 250 that covers nearly the entire coilpole treatment surfaces 22, 24 of the TMS coil assembly 20. A graphicdisplay of display 40 could then be used to guide the operator inplacement. The uniqueness of this application of variable resistancesensors is the magnetic environment and the specific geometry required.The resistance of the Sensors 240 must be relatively high to avoid largeinduced currents from the TMS pulse and the cross section of theconductive areas must be small to avoid eddy current heating.

During operation, the microprocessor 190 scans the intersecting pointsof the sensor's rows and columns by selectively closing switches 260,265 under control of control circuit 270 and measures the resistance ateach contact point. Each contact location is represented by a variableresistor 240 whose value is calibrated as a baseline reference when noforce is applied to it. The output of this data acquisition circuit 230is digitized by digitizer 280 and provided to microprocessor 190 wherethreshold detection is carried out. Microprocessor 190 then uses thepass/fail information for each sensor 240 to map the sensor states ontoa graphic display of display 40. Preferably, the array-based approach isconfigured with a graphic display map of the sensors 240 that clearlyindicate which sensors are activated (i.e. compressed) and which arenot.

Other Sensors That Detect Both Position and Contact Resistive Strip

The membrane switch 110 described above can be modified to provide anoutput voltage that varies with position of contact. In such case, thegap area 140 is extended to form a one dimensional gap instead of alocalized void. An external voltage is then applied to one of the films120, 130, and since no current is flowing, the entire film is atequipotential. When the films 120, 130 are pressed together, the upperfilm 120 is brought to the same potential as the lower film 130 at thepoint where contact is made. The voltage V1, V2 at the ends of the upperfilm 120 will depend on the location and spatial extent of the contact.These voltages can be converted into a reading of the location of thepressure along to the gap 140. A row of such strips can be placed in aparallel arrangement to make an area sensor 250. FIG. 8A shows a planview of such a strip sensor 290 before compression, while FIG. 8B showsa cross-section of such a strip sensor 290 after compression, where V1and V2 vary when the contact area is changed.

Touch Screen Technology

In a preferred embodiment illustrated in FIG. 9, touch screen technologyis similar to the strip sensor 290 (FIGS. 8A and 8B) except that theelectrodes 120, 130 of strip sensor 290′ are separated by an array ofseparators or non-conductive dots or strips (not shown). This allows thecontact to be sensed over an area. The position is read out by firstapplying a voltage V₁ along the horizontal direction and reading thevoltage the sensor film 290′ is pulled to and then applying a voltage V₂along the perpendicular direction and sensing the new voltage the sensorfilm 290′ is pulled to. One may also detect how large an area is incontact with the patient's skull by sensing the current between pairs ofelectrodes 120, 130 (i.e., the larger the current, the more area is incontact with the skull). Thus, the two dimensional position of thecontact can be sensed. The contract position is then mapped to agraphical display on display 40 as previously described.

Pickup Loop

As illustrated in FIG. 10, a loop or loops of conducting material 292may be affixed to the patient's head at the position for the motorthreshold (MT) procedure and/or a loop or loops of conducting material294 may be affixed to the patient's head at the position for depressiontreatment. Then, when the TMS coil assembly 20 is placed in the properposition, a pulsed magnetic field applied by the TMS coil assembly 20induce voltages in the loop or loops 292 or 294. If the patient movesaway front the TMS coil assembly 20 during the TMS procedure, then theinduced voltage in the loop or loops 292 or 294 is reduced. A thresholdcan be determined by the signal processing circuitry 80 for maintainingan effective treatment, and if the voltage drops below this threshold, avisible or audible signal is provided to the operator so that the TMScoil assembly 20 can be properly repositioned for the remainder of thetherapy.

Fluid Displacement Sensors

Fluid displacement sensors may be fabricated on a flexible, disposablesubstrate (e.g., polyester) 300 as illustrated in FIG. 11A. As shown,fluid filled bladders 310 are connected by a non-compressible manifold320 such that compression of one or both of the fluid filled bladders310 causes a change in pressure at fluid displacement sensor 330 that isdetected provided via connector 340 to the signal processing electronics80. As illustrated in FIG. 11B, the fluid displacement sensors also maybe manufactured on the same physical substrate 350 as an e-shielddevice. The fluid filled membrane bladders 310 are positioned directlyover the coil pole treatment faces 22, 24 of coil 360 as shown and areconnected to pressure transducer 330 for conversion of the fluidpressure into an analog voltage that is, in turn, connected viaelectrical connector 340 to signal processing circuitry 80 for theelimination of artifacts and detection of whether a threshold has beenexceeded, thereby indicating proper contact on both sides of the coil360. The fluid is high-impedance and provides for a minimal current flowand is, accordingly, substantially non-electrically-conductive so thatinduced eddy currents (due to the pulsing magnetic field) do not causeheating or field distortion. E-shield connectors 370 provide a mechanismfor driving, the e-shield coils from a remote pulse generator.

Optical Sensors

Optical sensors may be created by fixing an optical fiber 380 to theflexible substrate 300 such that it crosses the critical contact areaover the coil pole treatment faces 22, 24. Multiple optical fibers maybe used to isolate a particular location. Light from a remote lightsource 390 is provided into optical fiber 380 and directed toward afiber Bragg grating 400 as illustrated in FIG. 12A. When the light makescontact with the fiber Bragg grating 400, the fiber(s) of the fiberBragg grating 400 shown in cross-section in FIG. 12B deflect asillustrated in FIG. 12C so as to affair light transmission efficiency.For example, the reflectance peak may be shifted to longer wavelengthsas shown in FIG. 12D, which is, in turn, detected by an optical detector(e.g. photodiode) 410 (FIG. 12A). Thus, the fiber Bragg grating 400 isattached to the flexible substrate 300 in such a way that deflectionchanges the amount of light reflected from the fiber Bragg grating 400.Light is reflected off of the flexible substrate 300 so that it vibrateswhen magnetically pulsed. The modulation of the light is measured. Whenvibration is minimal, contact is good. A thin liquid-filled bladder(e.g., bladder 310 of FIG. 11A) may be applied to the flexible substrate300 and positioned such that contact at the critical areas of the coilpole treatment faces 22, 24 results in compression of the bladders 310on both sides of the coil 360 which, in turn, displaces liquid to anoptical detector 410 that detects the displacement, in accordance withthe invention, the optical detector 410 may include a photodiode, itphoto transistor, and the like.

Acoustic Sensors

Acoustic sensors may be mounted on the e-shield as in the embodiment ofFIG. 11B so as to produce an acoustic sound when pulsed. This sound isreduced in magnitude and the frequency shifts when compressed againstthe head. The acoustic sensors detect the change in sound level. Anychange is determined by processing circuit 80 (FIG. 2) or signalprocessing software.

FIG. 13A illustrates a sample acoustic sensor embodiment in whichflexible membranes 420, 430 in a non-contact position are separated byan acoustic channel 440 that, in turn, connects an acoustic source 450to an acoustic transducer 460. As shown in FIG. 13B, when the flexiblemembranes 420, 430 are pressed (against the head, for example), theacoustic channel 440 is disrupted, thereby reducing the sound inmagnitude and/or causing a frequency shift. Those skilled in the artwill appreciate that the acoustic source 450 and acoustic transducer 460may produce and detect sounds in the audible range and/or the ultrasonicrange.

Another type of acoustic sensor may be implemented as a deviceconstructed on the substrate 350 (FIG. 11B) so as to intentionally“rattle” or makes an obvious audible sound when the TMS coil is pulsedand the substrate is not compressed against the patient's head. Asillustrated in FIG. 14A, such a device includes flexible membranes 470,480 that are separated by spacers 490 so as to define a cavity 500between the flexible membranes 470, 480. The cavity includes aconductive disk 510 that experiences torque as indicated by the arrowsso as to rattle within cavity 500 when the ambient magnetic field ispulsed. As illustrated in FIG. 14B, the device is designed tosignificantly damp the sound when compressed against the head. In thiscase, the flexible membranes 470, 480 immobilizes the conductive disk510 to prevent raffling within the cavity 500 when the flexiblemembranes 470, 480 are compressed (e.g., against the patient's head).The audible feedback (e.g., lack of rattling sound) is the indicator tothe operator that the coil is in contact with the patient's head. Sincethe sound is audible, no acoustic sensors are necessary.

As illustrated in FIG. 15, an acoustic transducer 520 (audible orultrasonic) may be mounted or attached to the patient's scalp at aposition away from the magnetic field generated by the TMS coil assembly20 so as to detect sound waves conducted through the skull that aregenerated by the TMS coil within the TMS coil assembly 20 when pulsedand mechanically coupled to the skull through contact with the patient'shead. When the TMS assembly 20 is pulsed it generates an audible orinaudible vibration. When the TMS coil assembly 20 is in good contactwith the skull, this sound is transmitted effectively to the skull whichin turn is detected by acoustic transducer 520 applied to the patient'shead at a convenient location (typically not directly beneath the coil).The output of the acoustic transducer 520 is applied to signalprocessing electronics (which may be in signal processing electronics80) to detect a large change in the conducted sound has occurred,thereby indicating a disruption in the contact with the skull. Thecharacteristics of the received sound wave varies (e.g., spectral shiftor amplitude change) in accordance with the degree of mechanicalcoupling of the TMS coil assembly 20 with patient's skull. For example,low frequency waves are attenuated when the TMS coil assembly 20 is notin direct contact with the patient's skull, thereby changing theacoustic signature of the signal generated when the TMS coil is pulsed.

Inductive Coupling Sensors

To implement inductive coupling sensors, a tuned coil 530 is mounted tosubstrate 60 as shown in FIG. 16A. The tuned frequency shifts asillustrated in FIG. 16B when the substrate 60 and TMS coil assembly 20are in physical contact with the patient's head. Care must be taken todesign the tuned circuit so that it is compatible with the pulsedmagnetic field. The e-shield coils are pulsed independently from the TMScompensation pulse at a frequency that is sensitive to changes to coilloading (and corresponding changes in inductance). Changes in the coilcurrent waveform are detected and discriminated as to whether thee-shield is located against the patient's head or not. Compressibletuned coil 530 is mounted on the substrate and is designed so that itsshape (particularly its cross section with respect to the TMS field) isdistorted when compressed against the patient's head. In other words, adifferent induced current will be produced by a frequency counter whenthe compressible tuned coil 530 is compressed as compared to theuncompressed state. This induced current is then detected by signalprocessing electronics in signal processing electronics 80.

Capacitive Coupling Sensors

As illustrated in FIG. 17, EEG-type leads and electrodes 540, or theirequivalents, may be used to sense current induced in the scalp by theTMS magnetic pulse. If the TMS coil assembly 20 is moved away from thescalp, these currents will shift and diminish in amplitude. This changeis detected by processing the signals front the EEG-type leads 540 insuitable signal processing electronics. A minimum of two EEG-type leadsis required. Those skilled in the art will appreciate that carefulplacement of the EEG-type electrodes 540 and appropriate filtering thedetected signal in the signal processing electronics is important inorder to avoid artifacts due to patient movement or coupling with theTMS field.

Temperature Sensors

As illustrated in FIG. 18, temperature sensors (e.g., thermistors,thermocouples) 550 may be applied near the critical contact areas 22, 24on the substrate 60 and the outputs provided to processing circuitry(such as signal processing electronics 80) via connectors 155. Normally,the temperature of the two sides will track each other, however, if oneor more of the temperature sensors 550 is not in contact with thepatient's skull, there may be an unexpected abrupt temperature changeindicating a change in contact of the sensor(s) 550 with the skull. Inother words, if there is an unexpected significant change in thedifference or ratio of the two temperatures (i.e., if the change isabove a predetermined threshold), it is likely due to one side not beingin contact with the patient's head. On the other hand, if thetemperature detected by one or more temperature sensors 550 unexpectedlychanges abruptly, then this alone could indicate that the temperaturesensor(w) 550 is no longer in contact with the skull. This method hasthe disadvantage of a relatively slow response (i.e. several seconds).However, the unique advantage of this approach is the added feature ofallowing the operator to optimize TMS protocol parameters while stayingbeneath safe temperature levels. It can also be used as a safety featureto detect failures in the TMS system that could produce excessivetemperatures in the surfaces that contact the patient.

Those skilled in the art will appreciate that other sensing devices maybe used to determine whether the TMS coil assembly is properly placedagainst the patient's head during treatment. Accordingly, any suchmodifications are intended to be included within the scope of thisinvention as defined by the following exemplary claims.

1-44. (canceled)
 45. A magnetic stimulation system comprising: at least one magnetic stimulation coil assembly comprising at least one magnetic stimulation coil; at least one sensor configured to identify locations of a plurality of contact areas on the at least one magnetic stimulation coil assembly that are in contact with a patient's anatomy such that the contact areas on the least one magnetic stimulation coil assembly are distinguishable from non-contact areas on the least one magnetic stimulation coil assembly; and a processor to process outputs of the at least one sensor to provide an indication based on the locations of the contact areas on the at least one magnetic stimulation coil assembly that are in contact with the patient's anatomy. 